1. Field of the Invention
The present invention relates to a fluidized bed combustor, and particularly it relates to a fluidized bed combustor wherein a desulfurizing agent is mixed as a fluidized heat transfer medium and desulfurization of a combustion gas is carried out.
2. Description of the Prior Art
In conventional fluidized bed combustors, particles of heat transfer medium such as sand or cement particles are fluidized in a combustion chamber to form a fluidized bed, and a fuel such as coal, heavy oil, etc. is fed into the fluidized bed and burnt therein. When it is used for a boiler, a heat transfer tube through which water passes is arranged in the fluidized bed, and combustion heat generated in the fluidized bed is transmitted to the water inside the heat transfer tube.
Since coal or heavy oil employed as the fuel in the fluidized bed combustor has generally a high content of sulfur, it is necessary to remove sulfur oxides such as sulfur dioxide from the resulting combustion gas. Thus a desulfurizing agent such as limestone is usually blended therewith in the fluidized bed. The particles of such desulfurizing agent also function as a heat transfer medium. In the case where limestone is employed as a desulfurizing agent, it is decarbonated at high temperatures to form quick lime (CaO), which absorbs sulfur dioxide gas as shown by the following equation to effect desulfurization: EQU CaO+SO.sub.2 +1/2 O.sub.2 .fwdarw.CaSO.sub.4 ( 1)
Calcium sulfate formed by the desulfurization is sent together with the heat transfer medium to a regenerating furnace, where they are contacted with a reducing gas to effect regeneration, and then recycled to the fluidized bed in the combustor. In the case where carbon monoxide is used as a reducing agent, the reaction is expressed by the following equation (2): EQU CaSO.sub.4 +CO.fwdarw.CaO+SO.sub.2 +CO.sub.2 ( 2)
However, in the above-mentioned conventional fluidized bed combustor, since the combustor and the regenerating furnace are arranged separatedly, there are such disadvantages that the initial cost increases, and a circulating pipeline for transferring the fluidized medium containing the desulfurizing agent from the combustor to the separate regenerating furnace and then returning the desulfurizing agent regenerated therein to the combustor, and a power for supplying the above-mentioned medium, are required.